a) Field of the Invention
The present invention is directed to a rotary air coupling that provides a means to distribute air from an air supply to vehicle tires mounted on a rotating hub of a vehicle drive axle.
b) Description of Related Art
Automatic central tire inflation systems (CTIS) are becoming popular with the trucking industry. Various types of tire inflation system have been developed, both for trailer axles and tractor drive axles.
A central tire inflation system allows the operator to control the air pressure of the tires for improved performance of the tires and of the vehicle. However, the central tire inflation systems currently available suffer from two primary drawbacks. The axle and hub and possibly other parts must be extensively modified in order to accommodate a conventional system.
Central tire inflation systems in general are an important feature. Specifically, an off-road vehicle will often drive on soft, muddy surfaces and then switch to harder surfaces, such as paved roads. To obtain proper traction on soft, muddy surfaces, the tire should be operated at a relatively low pressure. To obtain proper traction and optimal fuel mileage on harder surfaces, the tires should be operated at relatively high pressures.
The differences between preferred high tire pressures (hard surfaces) and preferred low tire pressures (soft surfaces) may be quite large. For example, some truck tire manufacturers recommend a maximum tire pressure of 120 psi for highway conditions and 8 to 15 psi for extremely soft conditions such as sand, mud and swamps. A tire pressure for intermediate road conditions may be approximately 40 psi. Of course, in the case of trailers, the preferred tire pressure will also be dependent upon the weight of the goods or equipment carried in the trailer.
Another reason justifying the employment of central tire inflation systems is road surface deterioration. It is known that over-inflated tires are a major cause of road surface deterioration. Road repair and road building have become increasingly expensive and it is therefore foreseeable that governmental entities may begin penalizing the operators of trucks and tractor-trailers for operating equipment on public roads with improperly inflated tires or over-inflated tires.
Of course, another reason justifying central tire inflation systems is fuel economy. Soft tires on highways reduce gas or fuel mileage. A central tire inflation system that automatically controls the air pressures of trailer tires on a highway will increase fuel efficiency as well as improve road surface longevity.
Existing air distribution systems for tire inflation systems on drive axles direct the supply air through the bearings of the hub. Distribution through the bearings demand smaller bearings and require additional seals in the hub. The seal life is shortened due to the increased seal friction caused by pressure loading of the seal lips.
The need exists for a rotary air coupling designed to distribute supply air to the tires mounted on drive axles in which the air coupling is positioned externally of the drive axle and the hub bearings.
The present invention is particularly directed to a rotary air coupling designed to distribute supply air to the tires mounted on drive axles in which the air coupling is positioned externally of the drive axle and the hub bearings. Therefore, the improved rotary air coupling of the present invention by being mounted outside the bearings of the hub has no effect on existing hub bearings.
The present improved rotary air coupling takes advantage of the known dimension of existing wheel systems by connecting the stationary component of the coupling to the brake mounting plate directly or through the axle housing, while the rotary component of the coupling is press-fit onto the hub.
One of the advantages of the present invention is that the rotary coupling of the present invention does not interfere with the drive axle, bearings or lubrications as internal axle type air couplings can. Thus, there is no interference in the strength of existing vehicle components, which can lead to lengthy testing delays. Another advantage is the accessibility of the present rotary coupling. The present rotary coupling can be accessed as easily as brake shoes and will not cause mechanical difficulty in re-assembly.
The present invention is directed to an improvement in a rotary air coupling in a tire inflation system having a driven axle, a hub rotatable on hub bearings, a brake mounting plate, and a brake drum connected to the hub. The coupling includes an annular stationary housing positioned externally of the hub bearings, and connected to the brake mounting plate, and an annular rotatable housing positioned externally of the hub bearings and connected to the hub. Seal means are provided sealing between the stationary housing and the rotatable housing. An air supply inlet is connected to the stationary housing, and an air outlet is connected to the rotatable housing. The stationary housing and the rotatable housing include an air passageway therethrough communicating between the air inlet and the air outlet.
The present invention is further directed to the improvement in an air inflation system for tires on a vehicle having a driven axle with at least one pneumatic tire at each end of the axle, a hub rotatable on hub bearings, a brake mounting plate, and a brake drum connected to the hub of a rotary air coupling which distributes supply air to the tires. The rotary air coupling includes an annular stationary seal housing having a seal chamber with an radially facing opening in which the stationary housing is positioned externally of the hub bearings and connected to the brake mounting plate. The radially facing opening of the stationary seal housing and the radially facing opening of the rotatable seal housing are positioned adjacent to and face each other. A pair of stationary high pressure seals is provided having a sealing face and is positioned in the seal chamber of the stationary housing.
In an alternate embodiment, the present invention provides an improvement in a rotary air coupling in a tire inflation system having a driven axle, a hub rotatable on hub bearings, a brake mounting plate, and a brake drum connected to the hub. The alternative coupling includes a first annular housing mounted to the hub and rotor assembly using the rotor bolts, and a second annular housing press-fit on the axle tube. Seals are provided between the first housing and the second housing. An air supply inlet is connected to the stationary housing, and an air outlet is connected to the rotatable housing. The stationary housing and the rotatable housing include an air passageway therethrough communicating between the air inlet and the air outlet. For this alternate embodiment, compressed air passes through the same chamber as the parking brake is located in the rear disk brake configuration. This design allows for minimal change to existing production parts.
Other and further features and advantages will be apparent from the following description of a presently preferred embodiment of the invention, given for the purpose of disclosure, and taken in conjunction with the accompanying drawings.